1. Field of the Invention
This invention relates to a vibratory conveyor which conveys or transports material or various objects by vibration or solely by a sliding action.
2. Description of the Prior Art
In most vibratory conveyors which convey objects in a straight line, a trough is linearly vibrated in a direction which is slanted to the conveying surface. The objects are jumping repeatedly and are moved forward. The free flight of metal objects end with an impact which would increase noise. Free flight of the fragile objects ends with an impact which might lead to damage of the fragile objects.
In order to avoid these undesirable effects, the so-called "reciprocating conveyor" is developed in which the objects are conveyed solely by a sliding action, i.e., without leaving the surface of the conveyor. One example of the reciprocating conveyors is shown in FIG. 1 and is disclosed in the Japanese Opening Gazette 123812/1980.
A reciprocating conveyor 100 includes a trough 150 which is U-shaped in cross-section and vibrated by an exciter 110 in a horizontal direction. The objects are transported rightwards in the trough 150.
The trough 150 is supported on a base 109 through vertical leaf springs 152. The upper and lower ends of the leaf springs 152 are fixed to the trough 150 and the base 109 through fixing members 153a and 153b, respectively. The trough 150 is vibrated in the direction X by the exciter 110. The latter is combined with the former by horizontal leaf springs 129. The left and right ends of the leaf springs 129 are fixed to the exciter 110 and trough 150 through angular members 154 and 114 (FIG. 2). The leaf springs 152 are rigid in its longitudinal direction, while they are flexible in its lateral direction. Little force is applied in the vertical direction to the trough 150 by cooperation of the leaf springs 129 and coil springs 128 supporting the exciter 110 from the latter.
FIG. 2 is a plan view of the exciter 110 and portions relating thereto. FIG. 3 is a cross-sectional view taken along the line III--III in FIG. 2. As shown in FIG. 3, the exciter 110 consists of a pair of exciting mechanisms 131a and 131b which are attached to housings 111a and 111b (FIG. 1), respectively. They are fixed to each other through spacers 127 as one body, and supported on the base 109 through the coil springs 128.
The exciting mechanisms 131a and 131b are equal to each other in construction, and are arranged symmetrically with respect to each other. Only the construction of the exciting mechanism 131a will be described. A first rotational shaft 135a is supported by bearings 133a and 134a which are fixed to the housing 111a. A first semi-circular unbalance weight 136a of larger diameter is fixed to the first rotational shaft 135a. Similarly, a second rotational shaft 145a is supported by bearing 143a and 144a which are fixed to the housing 111a. A second semicircular unbalance weight 146a of smaller diameter is fixed to the second rotational shaft 145a.
An electric motor 121a is fixed on a back wall portion of the housing 111a. A belt 123a is wound on a pulley 122a fixed to a rotary shaft of the electric-motor 121a and another pulley 137a fixed to one end of the first rotary shaft 135a. A large-diameter gear 139a is fixed to another end of the first rotary shaft 135a, and engaged with a small-diameter gear 149a fixed to one end of the second rotary shaft 145a. The number of teeth of the small-diameter gear 149a is half of that of the large-diameter gear 139a. Thus, the second rotary shaft 145a is rotated in opposite direction to the first rotary shaft 135a, at the twice angular speed as the latter. Suffix b is attached to those of the other exciting mechanism 131b which correspond to the parts of the one exciting mechanism 131a, and the description of which will be omitted.
The first and second unbalance weights 136a, 136b and 146a, 146b of the exciting mechanisms 131a and 131b are fixed to the first and second rotary shafts 135a, 135b and 145a, 145b, respectively in the angular phase relationship as shown in FIG. 3. Accordingly, the composite force generated by the exciting mechanisms 131a and 131b, in the vertical direction Y is always equal to zero.
The construction of the reciprocating conveyor 100 of the prior art has been described. Next, its operation will be described.
The two first unbalance weights 136a are fixed to the rotary shaft 135a in the exciting mechanism 131a. However, they are equivalent in effect to the one first unbalance weight which is double in weight and is fixed to the center of the rotary shaft 135a. For simplification of the description, it is assumed that the one unbalance weight having the weight double as the first unbalance weight 136a is fixed to the center of the rotary shaft 135a. Similarly in the other exciting mechanism 131b, it is assumed that the one unbalance weight having the weight double as the first unbalance weight 136b is fixed to the center of the rotary shaft 135b.
Referring to FIG. 3, the electric motors 121aand 121b are rotated in opposite directions, in synchronization with each other. In the one exciting mechanism 131a, the first rotary shaft 135a is rotated in clockwise direction through the belt 123a, while the second rotary shaft 145a is rotated in anti-clockwise direction at the twice angular speed, since the larger gears 139a and the small gear 149a are engaged with each other.
In the other exciting mechanism 131b, the first rotary shaft 135b is rotated in anti-clockwise direction through the belt 123b, while the second rotary shaft 145b is rotated in clockwise directions at the twice angular speed, since the gears 139b and 149b are engaged with each other.
As shown in FIG. 4, the X-components Fax, Fbx of the centrifugal forces Fa, Fb generated from the first unbalance weights 136a, 136b in t seconds, are as follows: EQU Fa.sub.x =-Fa sin(.omega.t), Fb.sub.x =-Fb sin(.omega.t)
, where .omega. represents angular speed.
Accordingly, F.sub.x =Fa.sub.x +Fb.sub.x =-2Fa sin(.omega.t)
Similarly, the X-components fax, fbx of the centrifugal forces fa, fb generated from the second unbalance weights 146a, 146b,
fa.sub.x =fa sin(2.omega.t), are as follows: EQU fb.sub.x =fb sin(2.omega.t).
Accordingly, the composite force f.sub.x is as follows: EQU f.sub.x =fa.sub.x +fb.sub.x =2fa sin(2.omega.t)
Accordingly, the X-composite force Q.sub.x as whole,
Q.sub.x =F.sub.x +f.sub.x =-2Fa sin(.omega.t)+2fa sin(2.omega.t)
The trough 150 is excited by the force Q.sub.x. The Y-components Fay, Fby of the centrifugal forces Fa, Fb generated from the first unbalance weights 136a, 136b in t seconds is as follows: EQU Fa.sub.y =-Fa cos(.omega.t), Fb.sub.y =Fb cos(.omega.t)
The composite force F.sub.y is as follows: EQU F.sub.y =Fa.sub.y +Fb.sub.y =0
Similarly, the Y-component fay, fby of the centrifugal forces fa, fb generated from the second unbalance weights 146a, 146b are as follows:
fa.sub.y =-fa cos(2.omega.t), fb.sub.y =fa cos(2.omega.t)
Thus, the composite force f.sub.y is as follows: EQU f.sub.y =fa.sub.y +fb.sub.y =0
Accordingly, the Y-composite force Q.sub.y of the centrifugal forces generated from the first and second unbalance weights 136a, 136b, and 146a, 146b, are always equal to zero. EQU Q.sub.y =F.sub.y +f.sub.y =0
The composite force Q.sub.x is applied to the trough 150 only in the X-direction.
Q.sub.x =F.sub.x +f.sub.y =-2Fa sin(.omega.t)+2fa sin(2.omega.t).
In graph shown in FIG. 5A, axis of ordinates represents exciting force in the X-direction, and axis of abscissas represents time. The composite forces Q.sub.x, F.sub.x and f.sub.x change with time, as shown in FIG. 5A, where F.sub.x =2f.sub.x.
The reciprocating conveyor 100 is composed of one-mass system, according to the theory of the vibration technology. The resonant frequency of the reciprocating conveyor 100 is determined by a spring constant of all of the leaf springs 152, and a mass supported by the leaf springs 152.
When the spring constant of all of the leaf springs 152 is sufficiently small, and the trough 150 is vibrated by the force of higher frequency than the resonant frequency, the phase defference between the force Q.sub.x and the displacement of the trough 150 is equal to 180 degrees. Thus, the trough 150 is displaced as shown by curve D in the graph of FIG. 5A. The trough 150 moves forwards to the point p at the lower speed and moves backwards to the point q from the point p at the higher speed. FIG. 5B shows schematically such changes. The exciting force overcomes the frictional force between the object to be conveyed, and the conveying surface of the trough 150 during the high speed backward-movement period T.sub.1 to T.sub.2. Thus, only the trough 150 moves backwards, and the object remands on the original position. The object and the trough 150 move together during the low spread period T.sub.2 to T.sub.3. Accordingly, the object is transported forwards.
The first and second unbalance weights 136a, 136b and 146a, 146b are rotated in the above described manner so that the trough 150 is vibrated only in the horizontal direction. The belts 123a, 123b and gears 139a, 139b are aranged in the exciting mechanism 110, which make noise. The exciting mechanism 110 is complicated in construction.
In the above-described reciprocating conveyor 100, the vibration of the trough 150 is non-sinusoidal and horizontal. The amplitude of the vibration is determined by the exciting force Q.sub.x which is generated by rotation of the first and second unbalance weights 136a, 136b and 146a, 146b. The exciting force Q.sub.x is determined by the centrifugal forces of the first and second unbalance weights 136a, 136b and 146a, 146b. The frequency of the exciting force Q.sub.x is determined by the rotational speed of the electric motors 121a, 121b which drive the first and second unbalance weights 136a, 136b and 146a, 146b. Thus, the rotational speed of the electric motors 121a, 121b and the centrifugal forces of the first and second unbalance weights 136a, 136b, and 146a and 146b should be adjusted to obtain a desired vibration. The construction should be changed. It is difficult to obtain an arbitrary vibration by the prior art exciting mechanism 110. Accordingly, it is difficult to adjust a transporting speed and it is impossible to adjust the exciting mechanism so as to transport objects efficiently.
In order to avoid the above described disadvantages, the assignee developed such a reciprocating conveyor that uses a linear motor as an excitor in which pole change of primary windings and polarity change-over are made at the same time (Japanese Publication number 35395/1779). However, this reciprocating conveyor generates the reaction force which is transmitted to the base through the linear motor. In order to avoid the disadvantage, it is described that two troughs are arranged in line with each other, and they are excited in opposite directions by the respective linear motors, in the same Publication. To cancel the reaction forces from each other, such a complicated control should be effected that the respective troughs are slowly moved forwards and rapidly moved backwards in synchronization with each other.